Supervisory control system



' Dec. 5, 1939. p BQSWAU Re. 21,284

SUPERVISORY CONTROL SYSTEM Original Filed May 27, 1952 14 Sheets-Sheet l CONTROL& SUPERVISION W- STOP W-ALARM com: KEY '9 INVENTOR HANS P. BOSWAU ATTO EY Deb. 5, 1939. H. P. BOSWAU Re. 21,284

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SUPEHVISORY CONTROL SYSTEM Original Filed May 2'7, 1952 l4 Sheets-Sheet 5 FIG-3- INVENTOR HANS P. BOSWAU ii a I.

ATTO EY Dec. 5,1939. H. P. soswAu 21,284

' SUPERVISORY CONTROL SYSTEM Original Filed May 27, 1932 14 Sheets-Sheet 4 F'ICr4 TO OTHER STATIONS INVENTOR HANS P. BOSWAU ATToRNEv Dec. 5, 1939. H. P. BOSWAU Re? 21,284

SUPERVISORY CONTROL SYSTEM Original Filed May 2'7, 1932 14 Sheets-Sheet 5 558 FIG- 5 INVENTOR HANS P. BOSWAU ATTOR 7 Dec. 5, 1939. H. P. BOSWAU 21,234

SUPERVISORY CONTROL SYSTEM I Original Filed May 27, 1932 14 Sheets-Sheet 6 FIG-6' INVENTOR HANS P. BOSWAU ATTORN Y Dec. 5, 1939. H. P. BOSWAU 21,234

SUPERVISORY CONTROL SYSTEM Original Filed May 27, 1952 14 Sheets-Sheet 1 AUX. SW.

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INVENTOR HANS P. BOSWAU Dec. 5, 1939. H. P. BoswAu Re. 21,284

SUPERVISORY CONTROL SYSTEM Original Filed May 2'7, 1932 14 Sheets-Sheet 8 SUBSTATION FIG-8 TRUNK- l 436 437 TRuux-z FIG-9 'IT IT OFFICE I FIRST SUBSTATION TIIIQSBGH LAST SUBSTATION I INTERMEDIATE SUBSTATIONS PARALLEL LINE CIRCUIT FIG: IO

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SUPERVISORY CONTROL SYSTEM 1932 14 Sheets-Sheet 11 Original Filed May 2'7,

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Original Filed May 27, 193? 14 Sheets-Sheet 12 .855 :4 if? I 1 2 2 is INVENTOR HANS P. BOSWAU l-r'm fi H. P. BOSWAU Dec. 5, 1939,

SUPERVISORY CONTROL SYSTEM Original Filed May 27, 1932 14 Sheets-Sheet l5 UTUE INVENTOR HANS P. BOSWAU ATTOR' Jomkzou zotkmmmo Original Filed May 27, 1952 14 Sheets Sheet 14 83 8 03 K22 2. L @1124 as.

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INVENTOR HANS P. BOSWAU um/DHE ATTO EY Reissued Dec. 5, 1939 UNITED STATES PATENT OFFICE SUPERVISOR-Y CONTROL SYSTEM Hans P. Boswau, Lorain, Ohio, assignor to The North Electric Mfg. Company, a corporation of Ohio 27 Claims.

My invention relates to signalling systems, and more particularly to supervisory control systems in which a plurality of substations are selectively I controlled and supervised over a single signalling channel.

In supervisory control systems where a large number of substations are to be supervised and controlled from a single dispatching ofiice, there I is often not more than one signalling channel available for operation. In such cases the system. must operate over a single trunk without any sacrifice of the safe-guarding features which insure synchronous operation without possibility of failures. Such safe-guarding is necessary in a supervisory control system where many operations, if improperly made, would entail serious consequences.

Accordingly, an object of my invention is to provide a supervisory control system for controlling and supervising a plurality of substations from a single dispatchers office over a single signalling trunk.

A further object of my invention is to provide a supervisory control system in which apparatus in a plurality of substations may be selected, controlled and supervised over a single pair of conductors by means of synchronous selecting apparatus at each of said stations.

Still a further object of my invention is to provide means in a supervisory control system for selecting, supervising, and controlling remoteapparatus used in a plurality of substations over a single signalling channel, the remote operations of the selected unit being dependent automatical- 1y upon a check at the dispatchers oflice of the selection made at the substation.

Another object of my invention is to provide means in a supervisory control system for supervising and controlling a plurality of remote sub-- stations to prevent interference with, or loss. of,

signals in the event that more than one substation or the dispatchers office and a substation attempt to signal over the same signalling channel simultaneously.

5 In many supervisory control systems, the conductors, over which the supervisory signals are sent, are paralleled with the power conductors in which the circuit breakers to be controlled are located. Surges in these power conductors are 50 often so severe as to inductively induce sufficient current in the signalling circuits to render them useless by the transmission of false signals at the very time when the circuit is most needed for use.

5 .Accordingly,an object of my invention is to provide means in a supervisory control system for preventing false operations in a supervisory control system due to currents induced therein by an. adjacent power line.

Still a further object of my invention is to pro- 5 vide a normally open-circuited supervisory control system for controlling and supervising a plurality of substations from a single central station.

Still a further object of my invention is to provide a supervisory control system in which the receiving apparatus in each of a plurality of remote stations are multiplied to a single signalling channel extending from the dispatchers office to each of the remote substations.

Still a further object of my invention is to pro- 15 vide means in a supervisory control system for controlling and supervising a plurality of remote substations over a single channel, with transmitting and receiving apparatus, individual to the remote substations, connected in series in the 20 single signalling channel. 1

Still a further object of my invention is to provide means for transmitting station-group, and unit selection code combinations of impulse conditions over a single signalling channel for se- 25 lecting one of said substations, one of a plurality of groups in the selected substation and one of a plurality of units in the particular selected group, for operation from a central dispatching point.

Still a further object of my invention is to pro- 30 vide means in a multi-substation supervisory control system operated over a single signalling channel for locking out all but a selected substation.

Still a further object of my invention is to pro- 35 vide means in the same apparatus at the substation to function either as a transmitter or a receiver in accordance with whether the station is to transmit or receive signals.

In the development of supervisory control 40 systems, the necessity for insuring accurate operation requires that, following each selection, a check be made of the selection. As a result, the number of circuits and relays increases and. results in complications of the system. It is accordingly essential, wherever possible, to simplify the circuit design and to reduce the number of apparatus as much as possible.

Accordingly, an object of my invention is to provide means whereby the counting relay chains need require only a single armature for the selecting operations.

Still a further object of my invention is to provide means whereby the same circuit which controls the station selection, may be used for controlling the check code for the station selection and the same circuit which stops the group and unit selection code also responds to the group and unit check code.

Still a further object of my invention is to provide means whereby a single armature on each of the counting relay chains functions to carry out all the necessary functions including selection, identification by means of the check code, and the operation of the selected unit.

In many instances, it is desirable to check the positions of breakers at the substations. If a single master check is provided for this operation, it will be necessary to check all the apparatus at each of the substations whereas the dispatcher may desire to check only one substation at a time.

Accordingly, another object of my invention is to provide means whereby in a multi-substation supervisory control system, the apparatus units at each of the substations may be separately checked.

There are other objects of my invention which, together with the foregoing, will appear in the detailed description of the invention given in connection with the drawings in which:

Figures 1 to 4 are the circuit diagrams ofapparatus employed at the dispatchers o-fiice;

Figures 5 to 7 are the apparatus employed at the substations;

Figure 8 is a circuit diagram of my invention diagrammatically showing the signalling conductor connected to a third station.

Figure 9 is a circuit diagram of my invention showing the line relays and transmitters connected across the line.

Figure 10 is a circuit diagram of a modified form showing the line relays and transmitters connected in series with the line.

Figures 11 to 16 are charts showing the sequence of relay operations when a remote unit is selected and controlled.

Figure 17 shows the manner in which Figures 1 to '7 should be combined to form a complete illustration of the system.

Generally, my invention comprises circuit arrangements at the oflice and at each of a plurality of substations by means of which apparatus at each of a plurality of remote stations may be supervised and controlled from the same office over a single signalling channel, consisting, in the embodiment shown, of a single trunk circuit. The apparatus at the oflice and each of the substations are normally in condition for receiving signals from any one of the other stations.

At the office, if a key operation is performed for controlling a remote apparatus unit, relays are operated in response to this key operation for switching the apparatus thereat into a transmitting condition; at the same time setting up on the relays a predetermined code to be transmitted. Thereafter, impulses are transmitted from the ofilce to the substation and as each impulse is transmitted, counting relays at the ofiice and the substations are successively energized. A predetermined relay, operating through the contacts of the counting chain and the code controlling relays, energizes when the proper counting relay has been energized to stop the transmission of further counting impulses. Thereafter, the oflice conditions itself for receiving impulses while the substation which has been selected transmits check impulses back to the office to indicate the selection. The particular substation which has been selected is determined by the energization of a relay (also through the armatures of the counting chain) which will condition that particular substation for sending back the check signals, and for selecting that station, whereas at all the other stations when the first set of impulses stops on the same counting chain relay, a relay is energized which locks out these other substations from further responses to signalling impulses.

Thereafter, the selected substation sends back to the ofiice check signals in accordance with the selected station which indicates the particular substation which has been selected. On receipt of these impulses at the office through the counting chain, a relay is again energized at the oflice which switches the office to a transmitting condition. The ofiice thereupon again transmits a code of group selecting impulses which operate the counting chains at both the office and selected substation.

At the office again, when the proper counting relay is energized, a predetermined relay is operated over the armatures of the counting relay and the group code controlling relay, which has been energized by the original key operation, and this stops the transmission of further group selecting impulses. At the selected substation the group selecting code which is received operates the counting chain to make a predetermined group selection and then starts to transmit back to the ofice a combination of impulses indicating the particular group selection which has been made. The office in response to this checking code, after an interval of time, again conditions itself for transmitting impulses and transmits the third or unit code selecting combination. This unit code combination is also stopped by a point code controlling relay which, as stated above, was originally energized in response to the key operation.

In the same manner, a check code is sent back from the substation indicating the unit selection and thereafter an operation control code is transmitted to operate the selected unit in the manner desired by the dispatcher and a supervising signal is sent back to the office indicating the final operation of the unit.

By means of this special circuit arrangement, the same signalling channel comprising in the embodiment shown, two trunk conductors, and the same counting chain or selecting apparatus at both the oflice and substation are utilized for the transmission of station selecting code impulses, group selecting code impulses, and unit selecting code impulses interposed by check impulses for the station, group and unit selection, and finally of the operation control code and supervising code. The same signalling conductors and, in fact, the same apparatus is also employed for the transmission of signals in the event of an automatic operation at the substations, for automatic release of the apparatus in the event of their failure in checking, for a reset operation from the ofiice and for any other desired function of a supervisory control system.

With the system in non-operating condition and normal, the relay A28 is energized over an obvious circuit including the back contact and armature 434. The relay 428 is a slow to dee ergize relay and is normally maintained energized during all operations to apply positive battery over the armature 435 at all times, except when the apparatus is to be restored to normal, as will be explained in detail hereinafter.

Normally, the relays 481 and 498 are also energized over a circuit from battery through the windings of relays 481 and 498 in series over the armature and front contact 488 of relay 494 and the back contact and armature 489 of relay 496 to positive battery. Although the relay 494 is at this time deenergized, its armature 488 is. held locked against its front contact by the latch member 460 which is controlled by the relay 495. The operation of this relay will be more clear from the description hereinafter.

Relays 498 and 48? control a switch circuit which throws the trunk conductors 432 and 433 in operative relation with the line relay 43! while at the same time associating a relay 484 with the alternate group of trunk conductors 436 and 431 for the purpose to be described in more detail hereinafter.

It will be noted. that relay III), which is. the supervisory relay individual to one of the points, is in an energized condition for indicating that the associated breaker at the remote substation is in a closed condition. On the other hand, relays III and H2, which are supervisory relays individual to other points, are shown deenergized to indicate a present tripped condition of their associated breakers.

Relays 585 and 582 are also normally energized over a circuit from negative battery through the windings of relays 585 and 582 in series, armature and front contact 592 of relay 589, and the back contact and armature 593, to positive battery. Although the relay 589 is at this time deenergized, its armature 592 is held locked in engagement with its front contact by the locking device 594 which in turn is controlled by the relay 59!.

Energization of the relay 582 associates the trunk conductors 432 and 433 with the line relay I over the armatures595 and 596. In the event of any difiiculty occurring, however, on the trunk conductors 432 and 433, the trunk conductors 43B and 431 may be substituted therefor by opening the circuit of trunk conductors 432 and 433 at armatures 595 and 596 and closing instead the trunk conductors 435 and 431 over the armatures of relay 583 to the line relay 5! I, and, at the same time, the trunk conductors 432 and 433 may be connected over the armatures of relay 584 to the relay 585. These operations will be described in more detail hereinafter.

The relay 598 at the substation is also normally energized at this time over an obvious circuit including the back contact and armature 533 of relay 559. The relay 598, which is the release relay, is normally energized and held energized during the stepping impulses, This relay is released only when the entire set is restored to normal. With the relay 538 energized, positive battery is applied to all points showing a single circle and positive symbol.

Relays 125, 126 and so forth, at the substation, are all normally energized, as shown, over looking circuits, which, in the case of relay 125, extend from positive battery over the armature 138 and its front contact of relay 125, armature 139 and its front contact of relay 129, through the winding of the relay 125, conductor 148, back contact and armature 186, to negative battery.

The locking circuits for the other relays 129 and so forth are completed over similar circuits including the armatures of their individual re-I,

lays, such as 12! and so forth. These individual relays 120, 12! and so forth, are individual to the breakers and are controlled by the auxiliary switch on their breakers. These relays are either energized or deenergized in accordance with the relays such as 125 are completed irrespective of the position of armatures such as 139 of the individual relays such as 129. The relays 125, 126 and so forth are point start relays which are momentarily released when their associated breaker changes its position from eitherclosed to trip or vice versa. When a relay such as 125 is momentarily released, it functions to start the apparatus at the substation into operation in a manner to be described in detail hereinafter.

The relay 499 at the office is also normally energized and looked over its own armature 492. This is the battery relay which is normally energized and releases only when the ofiice battery is interrupted for any reason. After release of this relay 499, as soon as the office battery comes back, the ofiice and all substations are automatically restored to normal by the operation of the release start relay 49! in a manner to be described in detail hereinafter.

In order to explain the operations in detail it will be assumed that the dispatcher desires to trip the breaker associated with the operating key I91. It will be noted at this time that the breaker associated with this particular point is in a closed condition since the relay III! is energized and an energizing circuit is completed for the red lamp E92 from negative battery, through the filament of the lamp I92, over the front contact and armature [21, to positive battery. Lamp I 92 is thus illuminated indicating a closed condition ,of this breaker.

The operator will now press the key I01 which will operate the contacts I98 and I99 into engagement with their respective contact points. This key, which is of the non-locking type, is momentarily depressed and thereafter automatically restored to its normal condition by spring action in any well known manner. As a result of the depression of key I91, an energizing circuit is completed for the relay229 from positive battery to the contact 698 into engagement at this point, conductor I28 through the winding of the relay 229, its armature 259 and back contact, and back contact and armature 260, to negative battery.

A further energizing circuit is completed for the relays 24! and 231 from positive battery over armature 294 and its back contact, back contact and armature 286, through the winding of the relay 24!, over the conductor 26!, the contact I99 in engagement with its contact point, conductor I29, through the winding of relay 231, armature and back contact 284, back contact and armature 293, to negative battery.

The relay 229 is one of a group of relays 226 to 235 which are the point code relays, one of which is energized when an operate key such as I9! is depressed and determines the code to be transmitted for making the point or unit selection.

The relay 23'! is one of a group of relays 231 to 249, which is a tens key relay and is energized when the operate key is depressed to determine the code to be transmitted for making the group or tens selection.

The relay 24! is one of a group of relays 24! to 244, which is energized when the operate key is depressed to determine the code to be transmitted for making a station selection, all of which will be described in detail hereinafter.

From the above detailed circuit description, it will be noted that one of the contacts, such as I08, controls the energizing circuit for the point selecting relay such as 229 whereas the other contact, such as I09, on the operate key is interposed between a group selecting relay 23? and station selecting relay 24f so that three relays, a-

point, a group, and a station relay, are all energized in response to a single key operation.

As a result of the energization of relay 229, a locking circuit is completed for this relay from positive battery over the front contact and armature 262, through the winding of relay 223, armature 259 and its front contact and the winding of the relay 236 to negative battery. The armature 259 of relay 229 being a make before break contact, as shown, will engage its front contact before breaking its back contact to insure completion of the above described circuit for the relay 236. Relay 2% upon energization, operates its armature 260 to disengage its back contact. Inasmuch as the energizing circuit for each of the point selecting relays 225 to 235 are all completed over the back contact of armature 263, no other of these relays can be energized in the event the dispatcher should for any reason depress a second operate key.

Furthermore, the locking circuit for the relay 229 now maintains this relay energized independently of the operate key, so this key may now be restored to normal without affecting the code to be transmitted.

As a result of the energization of relays and MI, a locking circuit is completed for these two relays from positive battery at relay 24 2, front contact and armature 285, through the winding of relay 24! the armature 28? of relay MI and its front contact, front contact and armature 264, through the Winding of relay 23?, armature 2% and its front contact, and through the winding of relay 245, to negative battery. Relay 2455 energizes and at armature 2% opens any further energizing circuit for the remaining group relays 238 to 24% and at its armature 294 opens the energizing circuits for the remaining station code controlling relays 242 to 244.

At the same time a starting circuit is completed from positive battery over the armature 294 and its front contact, armature 255 and its front contact, over the conductor 23 i, the back contact and armature 438 of relay 42!], armature and back contact 49211 and through the winding of relay M9, to negative battery. A multiple circuit is also completed with this circuit for the winding of relay 404 to negative battery. The relays 4M and 4 I 9 are start relays which are energized when an operate key is depressed and function to make the office end of the system the originating or transmitting end.

It will be noted that the above traced circuit for the start relays 404 and M9 is controlled by the armature 294 and 265 of relays 245 and 235, which are energized when the point, group and station code controlling relays are energized and locked in response to a key operation. The above traced circuit for the start relays 384 and 41d is also controlled over the back contact and armature 4fl2a of relay 402, which energizes as soon as the first line impulse is sent or received, in a manner to be described hereinafter.

The fact that armature 02m is in engagement with its back contact indicates that no substation signals are being received at this time and that accordingly the office end may seize the system for the transmission of selecting impulses. If, on the other hand, substation impulses were being received, the start relays 404 and H9 could not have been energized, even though the point,

group, and station code controlling relays had been energized in response to a key operation.

As a result of the energization of the start relay 304, a locking circuit for itself and M9 is completed over 4040 and an energizing circuit is completed for the relay 42's from negative battery thereat through the winding of relay Ml, back contact and armature MI, the front contact and armature 404a and armature 443 of relay M8 and its back contact to positive battery.

The relay 427 is a sending start relay which functions on energization to change the normal condition of the'system at theoffice end from a. receiving condition to a sending condition. In order to insure that this relay 42'! is not energized at a time when impulses are being received from the substation, its circuit is also completed over the back contact of armature Mil of relay 42!, which is energized during the period that impulses are being received from the substation. The circuit for relay 427 is also controlled by relay 418 for the purpose to be described hereinafter.

As a result of the energization of relay 421, an energizing circuit is completed for the relay 438 from negative battery, through the winding of relay 438, armature 4 34 and its back contact, armature 443i and it's back contact, and the front contact and armature 446 to positive battery.

The relay 438 is an impulse sendingrelay which is now about to send code combinations of impulses over the trunk conductors in accordance with the particular station, group and point selecting relays which have previously been. energized as described hereinbefore. The relay 630 will now be energized and deenergized intermittently in conjunction with the relay 425 over the armature 445, on which it will be recalled relay 436 found its energizing circuit.

As a result now of the energization of relay 43%], positive battery is applied over armature 441' and the conductor 448 to t e trunk conductor 432, and negative battery is applied over the armature 449 and conductor 450 to the trunk conductor 433. Energy from this same source is also applied across the line relay 43f at the ofice. Simultaneously energy is applied over trunk conductors 432 and 433 over front contacts and armatures 595 and 595 to the relay 5H at the substation. Accordingly, the line relays 43! and 5| l are energized simultaneously. The lin relays of other substations, as indicated in Fig. 4, are also energized.

As a result of the energization of line relay 43! at the ofiice, an energizing circuit is completed from positive battery over the armature 45! and. its front contact of relay 43!, through the Winding of relay 429 to negative battery.

The relay 429 upon energization now performs a number of functions among which is the energization of the first counting chain relay, which counts the first or blank step. The circuit extends from positive battery over the armature 434 and its front contact, armature 4:572 and its front contact, armature, 453 and its back contact, through the armature 32c and its back contact, armature 332i and its back contact, armature 322 and its back contact and through the Winding of relay 353 to negative battery. A multiple circuit is at the sametime completed over the conductor 323 and the back contact and armature 454 and the winding of relay 361!. Relay 402 is thereupon energized and operates its make-before-break armature 454 to engage its from negative battery through the winding of front contact and lock the relay 402 in energized position.

A further result of the energization of relay 429 is to open the energizing circuit for the slow relay 428 and at the same time to complete multiple energizing circuits for the two slow relays 425 and 426 over the armature 455 and its front contact.

As a result of the energization of relay 425, the energizing circuit for the relay 430 is opened at armature 445 and the slow relay 430 deenergizes after an interval of time. Upon the deenergization of relay 430, the line relays 43! and Eli are deenergized when armatures 441 and 440 disengage their front contacts. This is the end of the first impulse.

As a result of the deenergization of relay 43l, relay 429 deenergizes opening the energizing circults for relays 425 and 423 and reclosing the energizing circuit for relay 428. The relay 423 is a sufficiently slow relay so that it remains energized during the brief interval while the relay 429 Was energized.

The relay 303, upon energization, prepares a locking circuit for itself and relay 302 from negative battery through the winding of the relay 303, armature 324 and its front contact, through the winding of the relay 302, back contact and armature 325, and the front contact and armature 456, to positive battery. But this circuit is not effective at this time due to the direct positive battery obtained for the relay 303 at armature 434. At the end of the impulse period, however, when relay 429 deenergizes, as described above, this circuit becomesefiective and relays 303 and 302 energize in series. As will appear from the following, relay 302 acts as a switch-over relay to switch the next impulse for operating the counting chain to the next counting chain relay 304. Relay 429, upon deenergization, opens the energizing circuit for the relay 425. This slow relay, after an interval of time, again permits its armature 445 to engage its back contact,

whereupon the original energizing circuit for the relay 430 is again completed to transmit a second impulse. Relay 426 is slower than relay 425 and remains operated during intervals between impulses.

At the substation, in response to the energization of relay 5, an obvious energizing circuit is completed for the relay 509. Energization of the relay 509 completes an energizing circuit for the first counting relay 603 from positive battery over armature 533 and its front contact armature 534 and its front contact, armature 54! and its back contact, armature 529 and its back contact, armature 630 and its back contact, armature G3I and its back contact, through the Winding of relay 603, to negative battery. Relay 603, upon energization, prepares a locking circuit for itself and relay 602 at armature 633 and this circuit extends through the winding of relay 602 over the back contact and armature 034 and front contact and armature 503a to positive battery. This circuit, however, is not at this time completed because of the fact that the original energizing circuit for relay 603 provides a short circuit around the relay 602.

The original energizing circuit for the relay 603 is multiplied overthe conductor B60 and over break contact and armature 543 through the winding of the relay 5l4 to negative battery. Relay 5l4, upon energization, operates its makebefor-e-break armature 543 and this relay is locked over armature 543. At armature 545 an energizing circuit is completed for the relay 555 the relay 5l5, front contact and armature 545, back contact and armature 546, back contact and armature 569 to positive battery.

A further result of the energization of relay 509 is to complete an energizing circuit for the relay 503 from negative battery through the winding of the relay 503, back contact and armature 533, back contact and armature 335, front contact and armature 534, and front contact and armature 533 to positive battery and to open the energizing circuit for the relay 508, but relay 508 is sufficiently slow so that it does not deenergize in the interval while the relay 509 is energized during impulses.

Energization of relay 503 completes an obvious energizing circuit for the relay 502 which in turn energizes the relay 50l and relay 50l in its turn energizes relay 500. By this time the first impulse has been terminated at the office end and relay 509 is deenergized, in turn deenergizing the relay 503 Which is slow and remains operated betweenv impulses and again closing the energizing circuit for the relay 508.

Deenergization of the relay 509 opens the original energizing circuit for the relay 603 and this relay 603 energizes in series with the relay 602 as described above.

At the office, as a result of the deenergization of relay 423, following the deenergization of relay 430, an energizing circuit is again completed for the relay 428 before this relay has had a chance to deenergize. At the same time, the energizing circuit for the relays 425 and 420 is opened at armature 434 which disengages its front contact. Relay 425 upon deenergization, again closes an energizing circuit for the relay 430 at armature 445 and its back contact. Relay 430 is thereupon energized to transmit a second signalling impulse energizing the line relay 429 at the ofice and line relay 509 at the substation.

As a result of the energization of relay 429 for a second time, an energizing circuit is completed for the next counting relay 304. This circuit extendsover the circuit traced above for the first counting relay except that now armature 322 instead of engaging its back contact, engages its front contact and armature 326 is in engagement with its front contact so that the circuit extends to the relay 304. Relay 304, upon energization, prepares a locking circuit for itself and the relay 30! at armature 321. But this circuit is not effective at this time due to the original energizing circuit for the relay 304.

A further result of the energization of relay 429 is to again energize relay 425 which in turn opens the energizing circuit for the relay 430 at armature 445 to terminate the second impulse. Deenergization of the relay 430 in turn deenerglzes relay 423 whereupon the locking circuit for relays 304 and 30! becomes effective.

In this manner, impulses are transmitted over the line successively energizing the counting relays 303, 304, 305, etc., these relays being successively energized under control of the switch-over relays 300, 30I and 302.

Relay 30!, upon energization, opens the locking circuit for the relay 303 and 302 at the armature 325 which now disengages its back contact.

The relays 303 and 302 are now deenergized.

Upon the energization of relays 304 and 30! and upon the deenergization of relays 303 and 302, an energizing circuit is completed for the relay 4! from negative battery through the winding of the relay 4I8, armature 451 and its back contact, the front contact and armature 458, armature 266 and its front contact of the station code relay 241, conductor 261, conductor IEI, the front contact and armature 329 of chain relay 304, front contact and armature 330, back contact and armature 331, back contact and armature 332, conductor 334, armature 459 and its back contact, and armature 404?) and its front contact, to positive battery. Relay 4| 8 is the station sending control relay which operates when the proper number of impulses for station selection have been transmitted and functions when energized to stop the transmission of further impulses. One of the effects of the energization of relay H8 is to operate make-before-break armature 451 to lock the relay H8 in energized position and at the armature 443 the circuit of relay 421 is opened and relay 421 is thereupon deenergized. The deenergization of relay 421 in turn opens the locking circuit for the relays 304 and 3M and. these relays are now deenergized.

It will be noted that the relay 410 completed its energizing circuit over the armature of relay 24! which was energized in response to the key operation for controlling the station controlling code, and that this circuit was also completed over the armatures of relays 304 and 3M which were energized following the transmission of the correct number of station selecting impulses.

At the substation, it will be recalled that the last operation described was the deenergization of the relay 5| I following the termination of the first signalling impulse. Upon the deenergization of the relay 5| I, the relay 509 is deenergized which again closes the energizing circuit for the slow relay 508 so that this relay 508, which was deen ergized during the interval while the relay 509 was energized during the impulsing period, does not have time to deenergize during the impulsing interval and accordingly remains energized.

A further result of the deenergization of relay 509 is to open the energizing circuit for the relay 503 which, being a slow to deenergize relay cannot deenergize before relay 509 again energizes in response to the second impulse.

A further result of the deenergization of relay 509 is to open the original energizing circuit for the relay 603 and relay 503 now energizes in series with relay 602 over a. self-locking circuit. This circuit extends from negative battery through the winding of the relay 603, the armature 633 and its front contact, through the winding of the relay 602, the back contact and armature 634, and front contact and armature 5030. to positive battery. These operations occur at the end of the first impulsing period and before the second impulse, as described above, is impressed upon the trunk conductors.

At the substation, as a result of the energization of relay 509 in response to the second impulse received over the trunk conductors, the energizing circuit of relay 508 is again opened, but, as explained before, this relay is sufficiently slow in its operation so that it will not deenergize during this interval.

A further result of the energization of relay 509 is to complete an energizing circuit for the relay 503 over the circuit traced hereinbefore, and to complete an energizing circuit for the counting relay 604 from the negative battery through the winding of the relay 604, the armature 635 and its front contact, and front contact and armature 63L back contact and armature 630, back contact and armature 629, back contact and armature 54I, front contact and armature 534 and the front contact and armature 533 to positive battery.

In the second impulse period the relay 5 is again deenergized when the impulse over the trunk conductors terminates. the relay 5 in turn deenergizes the relay 509. Relay 509 upon deenergization, again completes the energizing circuit for the relay 508 before this relay has had time. to release and. open the energizing circuit for the relay 503 which, being a slow to deenergize relay, will drop out after an interval of time, since no further impulses are received at this time.

A further result of the deenergization of relay 509 is to open the original energizing circuit for the relay 604 as traced hereinbefore. Relay 004 will now energize in a series locking circuit with relay I from negative battery through the winding of the relay 50 1, the armature 035 and its front contact, through the winding of the relay 00L back contact and armature 631 and the front contact and armature 503a to positive bat-* tery.

Energization of relay 6! opens the series looking circuitfor the relays 603 and 002, which was previously traced, over the back contact and armature 634. Relays 503 and 602 are thereupon .deenergized.

It will be recalled that following the transmission of the second impulse over the trunk conductors, further impulsing from the oiiice was at this time stopped. Accordingly, a longer nonimpulsing period will be obtained during which the relay 509 remains deenergized than is the normal period between the Accordingly, relay 509 will be deenergized sufficiently long to permit relay 503 to deenergize. After an interval following the deenergization of relay 503, relay 502 is also deenergized.

A further result of the deenergization of relay 503 is to complete an energizing circuit for relay 181, the circuit extending from positive battery over the armature 531 and its back contact, armature 558 and its front contact, (relay 50! not having as yet dropped out), armature 541 and its back contact, armature 548 and its back contact, conductor 663, and through the winding of relay 181 to negative battery. It will be noted that this circuit is completed following the deenergization of relay 503 before relay 50! has had time to energize.

A circuit is now completed for relay 522 from negative battery through the winding of relay 522, conductor E08, armature 183 and its front contact, conductor 155, front contact and armature 640 of the counting relay 504 and thence to positive battery over the circuit already traced heretofore.

As the interval of non-impulsing continues, the relay 502 upon deenergization in turn opens the energizing circuit for the relay 550i which also deenergizes after an interval of time, the relay 50| in turn opens the energizing circuit for the.

contact, to positive battery.

Deenergization of 

